The operation of the powertrain in an automobile is one of the major contributors of noise received within the passenger compartment of the automobile. With new powertrain technology, such as electronic valve actuation and variable displacement engine, new methods are needed to control the interior noise. In order to improve customer perceived interior noise quality, passenger compartment active noise control has been a popular strategy for study. Such methods of noise control are discussed below relative to prior art documents. Generally, these methods are expensive and only control the receiving end of the problem such as the passenger driver's ear positions, which can affect the speech intelligence to the passenger. Other methods of controlling noise are directed to the source, such as an active control of the induction or exhaust systems, have been developed. However, active control capability is limited and is very complex and expensive. Therefore, active noise control systems have not proven to be popular even though the methodology and technical capability have existed for many years.
An example of active passenger cabin sound suppression technology can be found in U.S. Pat. No. 4,506,380 granted to Shinichi Matsui on Mar. 19, 1985, in which speakers disposed in the dash panel of the vehicle are individually energized to selectively control the resonance occurred with respect to engine vibration. Similarly, an active vibration/noise control system in taught in U.S. Pat. No. 5,386,372, issued on Jan. 31, 1995, to Toshiski Kobayashi, et al, wherein speakers are arranged in suitable locations in the dashboard of the passenger compartment to control the noise from the engine. Self-expanding engine mounts have actuators formed of piezo-electric elements or magnetostrictive elements to prevent the vibrations from being transmitted from the engine.
Passive sound-absorbing materials are utilized throughout an automotive vehicle to reduce noise transmission. An example is found in U.S. Pat. No. 7,017,250, issued to Girma Gebreselassie, et al, on Mar. 28, 2006, wherein a dash insulator system has a substrate made from foam that is used to absorb the sound directed to a dash insulator. In U.S. Pat. No. 4,574,915, granted to Heinemann Gahlaii, et al on Mar. 11, 1986, sound-insulating cladding, formed from viscoelastic foam material is secured on the face of the front bulkhead to provide a sound-insulated area. Sound absorbing materials are used in the dashboard area of the vehicle to provide a passive noise control system preventing the noise generated in the engine compartment from being transmitted to the passenger compartment, as is suggested in U.S. Pat. No. 5,094,318, granted to Takashi Maeda, et al on Mar. 10, 1992; in U.S. Pat. No. 5,554,831, granted to Hiroshi Matsukawa, et al on Sep. 10, 1996; in U.S. Pat. No. 5,817,408, granted to Motohiro Orimo, et al on Oct. 6, 1998; in U.S. Pat. No. 6,102,465, granted to Kouichi Nemoto on Aug. 15, 2000; and in U.S. Pat. No. 6,554,101 granted to Kyoichi Watanabe on Apr. 29, 2003.
An isolator system, comprised of cast foam, is affixed to horizontal and vertical portions of the vehicle dash panel to reduce the transmission of unwanted noise and vibration from the engine compartment is taught in U.S. Pat. No. 6,767,050 granted to Christian Junker on Jul. 27, 2004, and assigned to Ford Global Technologies, LLC, and in U.S. Pat. No. 7,070,848 granted to Michael Campbell on Jul. 4, 2006. An automotive dash insulator system, used to reduce noise transmission from the engine to the interior of the vehicle, is formed with a sound-absorbing layer comprised of viscoelastic foam as depicted in U.S. Patent Application Publication No. 2005/0150720, of Jay Tudor, et al, published on Jul. 14, 2005.
A noise control system using a piezo-electric control scheme can be found in U.S. Pat. No. 6,589,643, granted on Jul. 8, 2003, to Jun Okada, et al, in which sound absorbing material, such as piezo-electric material, is used to insulate a dashboard in a vehicle to absorb and prevent the entry of low-frequency noise from the engine into the passenger compartment. In U. S. Patent Application Publication No. 2004/0130081 of David Hein, published on Jul. 8, 2004, a piezo-electric actuator and sensor assemblies are introduced between various structures contained within the instrument panel to minimize vibration within the instrument panel structure.
Adaptive filters have also been used to control noise generated from a noise source, such as the engine in an automobile, as taught in U.S. Pat. No. 5,131,047, issued to Hiroyuki Hashimoto, et al on Jul. 14, 1992, where a speaker is utilized to reproduce engine noise that controls the generated engine noise. In U.S. Pat. No. 5,321,759, granted to Yi Yuan on Jun. 14, 1994, adaptive filters having transversal filters are utilized in an active noise control system to control engine generated vibrational noise. A directional microphone is integrated into the dashboard to achieve a directional effect for controlling automotive noise is taught in U.S. Pat. No. 6,305,732, granted on Oct. 23, 2001, to Hans-Wilheim Ruhl. In U.S. Pat. No. 6,324,294, issued on Nov. 27, 2001 to Henry Azima, et al, loud speaker panels are attached to or installed in the dashboard of an automobile. U.S. Patent Application Publication No. 2004/0240678 of Yoshio Nakamura, et al, published Dec. 2, 2004, discloses an active noise control system that uses a speaker to control problematic noise generated by the engine.
It would be desirable to provide a system for reducing engine noise that is directed to the transfer path, rather than the source or the receiver of the noise. It would also be desirable to provide a system that utilizes a box-like structure imposed transversely across the transfer path so that the natural acoustic resonance of the structure can be utilized to aid in the control of the transmitted noise.